Aerial propeller.



G. M. OLMSTED.

AERIAL PROPELLER.

APPLICATION 31mm OUT. 2, 1909.

1,019,078, Patented Mar.5, 1912.

CHARLES-MORGAN o'mu s'run, or PASADENA, camromua- AERIAL PnorEL'Lnn.

' Specification of Letters Patent. -Pa,tefl te 1Maf; 5; 1912,

Application filed ctober2, 1999'. Serial Nd. 520,677.

To all whom it may concern: Be it known that I, CHARLES M. OL s'reo, .of Pasadena, in the county of Los Angeles and State of California, have invented certain new and useful Improvements in Aerial Propellers; and I do hereby declare the following to be a full, .clear, and exact description of the invention, such as will enable others skilled intheart to which it apper- 1 0 tains to make and use the same.

' :1 cation relates more especially to propell for the propulsion, support .or

ontrol-ioffaerial craft such as so called it/has generally been the cuserial' craft, to formthesei of two es or vanes so proportioned that 'shal l 'i;be determined by the intersecfthe-surface of'the helix with two parf :"plane's,which are perpendicular to the s. of the helix; that is to say, the blades fwiden toward the peri hery of the propeller. well known to t ose familiar with the art, the energy used inturning 'a'propeller 'ofthis'kiiidfor a given time 1s more than -the' fgwork represented by thepull of the propeller multiplied by the"dis tance' through p, which it moves its load in this time; the ratioofthe'work done to the energy used beii igfknown'as the efliciency of the ropeller. ,g'fJ It' is also known that. various loa s require t moved with a'maximum of efiiciency. It is not generally known, however, that by departing from he describedpoinmon form of helical propeller an eificiencygreater than that obtainable with the' aforesaid propeller may be secured. The object of this inventionfis to secure such increased efficiency, and this 'I accomplish by so designing the propeller blades "thatevery. element of the blades will act upon the air 'in the most economical manner possible. I have discoveredthatvithis maximum efficiency maybe attained by construct- 9 equation:

' (r tan.( e) P) a r(cos. ar'sec. (d-s a where a' tan.

In (1). a represents the total width of 'fl ying jnachines-f as well as helicoptic orv employing helical propellers osteriorfgland anterior edges of these various sized and pitched propellers to be 'ing a propeller whichifulfils the following all of the blades at any distance r from the axis of thepropeller; a the angle which the surfaceifof the blade makes with theplane of the propeller (the surface being understood to mean not. necessarily the 'physical'surface of the blade at the point in uestion; but a plane to which the resultant orce of the air pressure is perpendicular when the relative motion 'of air and blade is such that this resultant pressure is as near being perpendicular to the direction of related motion as it is possible, with the iven blade,.to make it.) C, the constant which, de-

termines the pitch of' the helix, obtained as hereinafter described; P, the distance which radian is C times the pull, and the work done b the propeller is P times-the pull.

.' The e ciency of the propeller is therefore I C For any given valve of G the pull of a helical propeller is maximum when Equation 1) describes th distribution and angle of blade surface, no matter how the diameter .of the propeller may be restricted on account of mechanical reasons. In practice these, propellers may be made the propeller advances during a turn of one 1 x radia'n'yand k ands constants determined as hereinafter described. In such a pro- ;peller, the-work of turning the propeller one with two or more blades symmetrically placed about the center. The plan of any particular blade makes little difference so long as the total width, at any distance from the center, of all the blades is of such an amount as to satisfy Equation (1).

The cross-section of the blades may be straight or curved as hereinafter described.

I prefer the latter form, however, since it makes the constant la in Equation (1) smaller. By cross-section I mean the intersection of the blade with a cylindrical surface generated by revolving a line parallel to the axis of the propeller about said axis.

In order to construct a propeller according'to my invention one may proceed as follows: If, as is generally the case, the resistance of the aerial craft which is to be moved is such a function ofthe. velocity that it increases when the velocity increases, there will be a certain maximum speed with which a given amount of power-can drive the craft. If the amount of power available is fixed, it

is desired to obtain this maximum speed:

Or, on the other hand, if a certain speed is desired, it is desirable to obtain it with a minimum of power. We shall consider the latter case.

As the speed of advance is fixed, 0P is" fixed; a) being the angular velocity of rotation of the-propeller expressed in radians.

per second. Now the total pull of the propeller is the integration being extended over all regions where r tan. (oce),-1P is positive if there are no restrictions as to the maxi-' mum allowable diameter; or .over all such positive regions within this limit when it exslowness of revolution: First, if the propeller is attached directly to the englne shaft, 0) is at once fixed by the speed of the engine. Second, if the propeller is geared down, a maximum for o) is fixed by the available space for the propeller.

When (J) has been decided upon P becomes fixed. P being known, the value of C necessary to get the desired pull may be deduced from '(2), remembering 0:7" tan. z. It is preferred to do this by a series of trials resulting from the substitution of various values of C in (2). By interpolation the exact value of C necessary to produce a given pull can be found. C having been found, the value "of a for various distances from the center may be computed from (1). In this computation the values of a and in are determined experimentally. 1

Experiment (well known'to those familiar with the art) shows that the direction of the reacting force of the air may be brought to within 2 to 5 degrees of perpendicularity in the case'of planes orslightly concave surfaces. Call this angle a. a is then a small angle lying between 0 and say 5 in the caseof planes or slightly concave surfaces, and is always no matter what g the shape of the surface, .the minimum to which the angle between the direction of the pressure on a surface and a plane perthat pendicular to its motion may be brought. k is equal to where c is the pressure on a square foot of the most economical angle-that is to say when-the resultant pressure on the surface makes an angle s with the plane which is perpendicular to the line of relative motion of surface and air. The velocityof relative motion must be 1 -ft.'per sec.

As to the distribution of the total blade surface among the blades this may be done to suit the convenience of the designer. I

prefer, however, to have as few blades as is consistent with mechanical strength and balance, two blades being. suflicient, if these do not have to be excessivelywide at any point to fulfil theconditions of Equation (1). If the imposed conditions are such that two blades would have to be' excessively wide over part of theirextent, these may be made narrower where necessary, with blades- ,added to make up the required' amount of blade surface.

A plurality of specific forms of propeller constructed in accordance with my invention are shown in the accompanying drawings, wherein,

Figure 1, represents in frontelevation a the employed surface when this is held at I two blade form of the propeller; 2, a

rear elevation of said propeller; Flg. 3, a side elevation of said propeller, (here the dotted line indicates the theoretical boundary of bla'de where this does'not coincide with practical boundary), and, Fig. 4, a cross-section on. line 4-'4= Fig.1; Fig. 5, a cross-section of the propeller blade if made flat, and, Fig. 6, a front elevation of a form' of my improved propeller where more than two blades are employed.

The propeller shown in Figs. 1 to 5, consists, as will be seen, of twoblades 1 and 2, each of which increases in width from. a point near the axis of the propeller, or base of the blade, until a maximum is reached at a distance from the axis where the pitch angle of the blades is greater than 45, and

then gradually decreasing from this point outward. In-.this propeller the blades are concavo-convex as at 3, 4, along any crosssection, but; if desired, I may make the blades flat in cross-section as indicated in Fig. 5, this section being supposed to be taken at a point in the length of a fiat propeller blade corresponding to the point Where the section 4L is taken in a con cavo-convex blade.

In Fig. 6, I' have shown a form of my propeller to illustrate the case herein above mentioned where it becomes preferable on account of thetotal width of'blade required to fulfil the requirements of Equation 1),

amount of blade width. The two propellers which have been shown are only two of many specific shapes which may be included in the general scope of my invention.

As to application, these propellers are designed principally for the propulsion, support or control of aerial craft, including so called flying machines and helicoptic toys. The said propeller may, however, be used for any other desired purpose.

I claim as my invention:

1. An aerial screw-propeller comprising a hub and a plurality of rigid blades, the contours whereof substantially conform to a helicoidal surface throughout their entire extent, and the cross sections whereof are concavo-convex wherever taken between hub and tip, each blade having its widest portion adjacent to said hub, and more than twice as wide as the width of that blade at a distance from the axis equalto three-fourths of the extreme radius of the propeller.

2-. An aerial screw-propeller comprising a hub and a plurality of rigid blades, the contours whereof substantially conform to a helicoidal surface throughout their entire extent, and the 'cross sections whereof are concavo-convex wherever taken between hub and tip, each bladehaving its widest portion adjacent to said hub, and more than twice as wide as the width'of that blade, at a distance from the axis equal to three-fourths of the extreme radius of the propeller, and each blade directly connected to-said hub over a width greater than twice the width of that blade taken ata distance from the axis equal to three-fourths bfthe extreme radius of the propeller. f v

3.. An aerial screw-propeller having a plurality of rigid blades, every part of which conforms, as described, to a helicoidal surface, and each'of which so varies in width that more than sixty percent. of'thetotal amount of blade surface is included within a cylinder described about the axis, with a radius equal to onehalf the radius of the propeller, the variation in width being such that the radial gradation in total wldth is gradual.

4. An aerial screw-propeller havin a plurality of rigiclblades, everypart'o which conforms, as described to a helicoidal surface, and eachof which so varies in width that more than sixty per cent. of the total amount of blade surface is included within a cylinder described about the axis, with a radius equal to one half of the radius of the propeller, and so that more than twentyfive per cent. of the total amount of blade surface is included within a cylinder de-' axis, equal to scribed about the axis, with a radius equal to one fourth of theradius of the propeller, the variation in width being such that the radial gradation in tot-a1 width is gradual.

5. An aerial screw-propeller with rigid helicoidal blades which are wider at a dis-. tance from the axis equal to one fourth the radius than-they are at a distance equal to one half the radius, and which are more wide at a distance from the one half the radius as they are at a distance from the axisequal to three fourths of the radius.

6. An aerial screw-propeller having a pluthan twice as rality of rigid blades every part of which :conforms as described to a helicoidal surface and each' of which so varies in width that more than sixty per cent. of the total amount of blade surface is included within a cylinder described about the axis with a radius equal to one half the radius of the propeller, the variation in width being such that the total width of blade surface increases gradually to a maximum close to the hub, then decreases, at first slowly then rapoached.

rality of rigid blades every art of which conforms as described to, a hehcoidal surface and each of which so varies'in width that -morethan sixty per cent. of the'total amount .andwhich gradually decrease at first slowly,

then rapidly, and then slowly toward the tip, the decrement in width growing at first gradually more and then gradually less, as" the ti is approached.

i 9. X. screw-propeller comprising a plurality of helicoidal blades, and in. which the total width of blade gradually increases from the axis toward the periphery until a maximum is reached at a distance from the axis where the pitch angle'is more than forty-five degrees, and then decreases from this point outward.

10. A screw-propeller comprising a plurality of-helicoidal blades, and inwhich the total width of blade gradually, increases from the axis toward the periphery until a maximum is reached at a distance from the idly, and finally again slowly as the tip s 'An aerial screw-propeller having a p ludecrease growing atifirst gradually greater,

and then gradually less, asthe extreme radiu s, or tip, is approached.

11. A screw-propeller comprising a plurality of helicoidal blades, and in which the total width of blade gradually increases from the axis toward the periphery until a maximum is reached at a distance'from the axis where the pitch angle is more than forty-five degrees, and then decreases from this point outward, and in which the wide bases of the blades, adjacent to the hub, are

directly attached to the hub.

12. A screw-propeller comprising a plurality ofhelicoidal blades, and in which the total width of blade gradually increases from the axis toward the periphery, until a maximum is reached at a distance from the axis where the pitch angle is more than forty-five degrees, and then decreases from this point outward, the rate of increase growing gradually less as the maximum width is approached, and then the rate of decrease growing at first gradually greater and then gradually 'less, as theextreme radius or tip is approached, and in which the i Wide bases of the blades adjacent to the hub,

- are directly attached to the hub.

13. A screw-propeller comprising a plurality of helicodial blades, and in which the total width of blade gradually increases from the axis toward the periphery, until a maximum is reached at a distance from the axis where the pitch angle is more than forty-five degrees, and then decreases from this oint outward, the rate-of increase growing gradually less as the point of maxiv lers, and in which more than twenty-five per cent. of the total amount of the blade surface is included within a cylinder described about the axis with a radius equal to onefourth of the radius of the propeller, and in which the total width of the blade, at a distance from the axis .equal to one fourth of the radius ofthe propeller, is greater than the total width of blade, at a dlstance from the axis equal to one half the radius of the r0- peller, and in which the total width of blade at a distance from the axis equalto one half the radius 'of the propeller, is more than twice as great as is the total width bf blade at a distance from the axis which is equalto three quarters of the radius of the propeller.

14. An aerial screw-propeller comprising a-plurality of rigid blades which differ in shape one from another, and each of which is twisted longitudinally so that the resultant of all pressures, at any given distance from the axis, is substantially perpendicular to thehelicoidal surface at such distance, and each of which is so graduated in width, that the total width of blade surface is greatest near to the axis, and decreases graduallytoward the tip of the blade, the graduation in width being at such a rate that more than half of the blade surface is located within a cylindrical surface described about the axis, with a radius equal to half of the radius of the propeller.

15. aerial screw-propeller comprising a plurality of rigid blades which differ in size one from another, and each of which is twisted longitudinally so that the resultant of all pressures, at any given distance from the axis, issubstantially perpendicular to the helicoidal surface at such distance, and each of which is so graduated in width, that the total width of blade surface is greatest near the axle, and, decreases gradually toward the tip of the blade, the graduation in width being at such arate that more than half of the blade surface is located within a cylindrical surface described about the axis, with a radius equal to half the radius of the propeller. 16. An aerial screw-propeller comprising a plurality of rigid blades which diiferin size and shape one from another, and each of which is twisted longitudinally so that the resultant of all pressures, at any given distance from the axis, is substantially perpendicular to the helicoidal surface at such distance, and each of which is graduated in width that the total width of blade surface is greatest near the axle, and decreases gradually toward the tip of the blade, the graduation in width being at such a rate that more than half of the blade surface is located within a cylindrical surface described about the axle, with a radius equal to half of the radius of the propeller.

17. A screw-propeller comprlsing a plurality of helicoidal blades, and in which the total width of blade gradually increases from the axis toward the periphery until a maximum is reached at a distance from the axis where the pitch angle is more than forty-five degrees, and then decreases from this point outward, the distribution of the blade surface being determined by and substantially conformable, over the greater part of its extent, to the rule:

r tan. (0l-e) P (JP-k 1' cos. a sec. (ae) wherein a is the total width of blade surface at the distance R measured perpendicularly from the axis of the propeller; k and P are constants determlned in the manner described; a is the quantity In testimony whereof, I have signed this determined in the manner described, and specification in the presence of two subscribing Witnesses.

' I CHARLES MORGAN OLMSTED.

- =tan. 5 r Witnesses:

Where C is a'constant determined in the JUAN R. GOMEZ,

'manner described. JAMES C. MORGAN. 

